Viscum

They are woody, obligate hemiparasitic shrubs with branches 15–80 centimetres (5.9–31.5 in) long. Their hosts are woody shrubs and trees. The foliage is dichotomously or verticillately branching, with opposite pairs or whorls of green leaves which perform some photosynthesis (minimal in some species, notably V. nudum), but with the plant drawing its mineral and water needs from the host tree. Different species of Viscum tend to use different host species; most species are able to use several different host species.

The flowers are inconspicuous, greenish-yellow, 1–3 millimetres (0.039–0.118 in) diameter. The fruit is a berry, white, yellow, orange, or red when mature, containing one or more seeds embedded in very sticky juice; the seeds are dispersed when birds (notably the mistle thrush) eat the fruit, and remove the sticky seeds from the bill by wiping them on tree branches where they can germinate.

Toxicity in the genus Viscum

Viscum species are poisonous to humans; eating the fruit causes a weak pulse and acute gastrointestinal problems including stomach pain and diarrhea. At least one of the active ingredients is the lectin viscumin, which is intensely toxic. It inhibits protein synthesis by catalytically inactivating ribosomes. In spite of this, many species of animals are adapted to eating the fruit as a significant part of their diet.